Method of making permanent magnet rotor for a synchronous motor

ABSTRACT

A permanent magnet is carried by two sections of a hub, the sections being bonded together by welding.

United States Patent [1 1 Bannon METHOD OF MAKING PERMANENT MAGNET ROTORFOR A SYNCHRONOUS MOTOR Inventor:

Albert C. Bannon, Indianapolis, Ind.

Assignee: P. R. Mallory & Co. Inc.,

Indianapolis, Ind.

Filed: Dec. 10, 1973 Appl. No.: 423,183

Related US. Application Data Division of Ser. No. 342,072, March 16,1973.

US. Cl. 29/598; 156/73; 310/42; 310/43; 310/156 Int. Cl. H02k 15/04Field of Search 29/598, 596, 608; 310/40 MM, 42, 43, 154, 156; 156/73Primary Examiner-Carl E. Hall Attorney, Agent, or Firm-Charles W.Hoffmann; Robert F. Meyer; Donald W. Hanson [5 7 ABSTRACT A permanentmagnet is carried by two sections of a hub, the sections being bondedtogether by welding.

3 Claims, 3 Drawing Figures mam-imam 81975 FJE Z METHOD OF MAKINGPERMANENT MAGNET ROTOR FDR A SYNCHRONOUS MOTOR This is a division, ofapplication Ser. No. 342,072 filed Mar. 16, I973 Generally speaking. thepresent invention relates to a rotor comprising a hub which includes atleast two sections bonded together, and a permanent magnet carried abouta periphery of the two sections. In general, the two sections are bondedtogether through welding, the welding, in the illustrative embodimentbeing accomplished by the application of ultrasonic vibrations.

The rotor of the present invention has particular utility in smallsynchronous motors.

There are a multitude of applications for small synchronous motors ofthe type having a small permanent magnet rotor. Many of theseapplications are in timing devices such as clocks or in appliances suchwashers and dryers which utilize time sequence switches. In suchapplications it is of prime importance that the various elements of thesynchronous motor be fabricated and assembled together at very closetolerances. And, even though very close tolerances are required, thecost of fabrication of the various elements as well as the cost of theirassembly should be kept at a minimum. Typical of such elements is thatof the rotor.

At one time the rotors were fabricated of a permanent magnet material inthe form of a disc, the disc being magnetized so that one face waspolarized north and the other south. The disc was then sandwiched between two metal spiders, the legs of which would then serve as polepieces of opposite polarity. This type of rotor was somewhat difficultto fabricate to close toler' ances and therefore somewhat costly. Ofrecent years, permanent magnet materials have been developed that permitpoles of opposite polarity to be impressed in their periphery. Thepolarlized permanent magnet is then secured to a support or hub. Variousmeans have been employed to secure the magnet to the hub including theuse of adhesives and insert molding. While this technique has been forthe most part satisfactory, the rotors still are somewhat costly duetothe cost of manufacturing to close tolerances.

Among the features of the present invention is the provision of apermanent magnet rotor which is easy to produce at close tolerances andtherefore relatively inexpensive. Another feature of the invention is toprovide a permanent magnet rotor for a synchronous motor. Still anotherfeature of the invention is the provision of a permanent magnet rotorhaving a permanent magnet carried by a hub that is comprised of at leasttow sections, bonded together. Yet another feature of the invention isthe provision of a permanent magnet rotor wherein a permanent magnet iscarried between two sections of a hub, the sections being weldedtogether. Yet still another object of the invention is the provision ofa permanent magnet rotor wherein a permanent magnet is carried betweentwo sections of a hub, the sections being ultrasonically bondedtogether. Still another feature of the invention is the provision ofpermanent magnet rotor wherein a permanent magnet is carried between twosections of a hub, the sections being ultrasonically bonded together,with the permanent magnet having means receiving material flowing fromthe sections as a result of the ultrasonic vibrations. Another featureof the invention is the provision of a method of forming a permanentmagnet rotor. And

LII

another feature of the invention is the provision of a method of forminga permanent magnet rotor wherein a permanent magnet is carried betweenat least two sections of a hub, the sections of the hub being bondedtogether.

These and other feature of the invention will become apparent from thefollowing description taken in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a section of a synchronous motor showing the rotor of thepresent invention;

FIG. 2 is a perspective view of a permanent magnet; and

FIG. 3 is a view showing the permanent magnet rotor prior to assembly.

Referring now to the drawings, the component parts of the presentinvention can be visualized. A synchronous motor M includes a top shell10 and a bottom shell 11 which are held together to form a housing. Thematerial for the shells 10 and 11 may be ordinary coldrolled steel,preferably annealed. Integral poles 10 and 22' are formed by lancingradial strips out of the flat portions of the respective shells andforming them parallel to the center axis to form a circle of pole tips.The poles that are formed in the shells constitute stator field polesand when intermeshed provide a stator assembly for the motor of thepresent invention. Tabs 21, lanced from shell 11, provide a means forconnecting a gear train housing (not shown) to the motor by engaging thetabs with cooperating apertures in the gear train housmg.

An energizing winding or coil 14, which includes an insulated spoolwound with a predetermined number of turns of wire, is annularlydisposed in the space between the ID of the shells 10 and I1 and theintermeshed stator poles 10' and 11' defining a circle. The wire iswound on a bobbin 13. Electrical leads 12 enables the coil to beconnected to an AC power source.

The rotor R of the synchronous motor includes a permanent magnet in theshape of a ring 17 carried by a hub 18. The permanent magnet includes amaterial of a relatively high energy product partial oriented ceramicsuch as a barium ferrite ceramic magnet with its outer periphery beingimpressed or magnetized into separate pole segments 19 of alternatenorth and south polarity. The permanent magnet material preferably hasan energy product of at least 1.4 X 10 gauss oersteds, and has arelatively large diameter to thickness ratio (about 4 to l) to provide ahigh torque in a thin package. A suitable material for the magnet couldbe a material manufactured by Stackpole Carbon Co. and designatedStackpole A-ZO, for example. As shown, the hub 18 is carried by an axle24 which is rigidly held to the top shell 10. Hub 18 is free to rotateabout the axle within sleeve 25. An output pinion 26 is formed as partof the hub 18.

The motor also includes a one-way directional means 30. One-waydirectional means 30 includes a member 32 in the shape of a cam carriedby the rotor hub 18 and a restraining member in the form of a pawl 34pivotally carried about post 36 which is fixedly carried by the shell10. Paw] 34 cooperates with cam 32 to stop the rotor from a wrong-waydirectional travel as will be hereinafter described.

In operation, when an AC current is applied to the coil 14, the rotor ofthe motor will begin to rotate due to the magnetic flux paths generatedbetween the rotor poles and the stator poles, the starting of the rotorbeing initiated by an asymmetrical arrangement of the stator poles. Oncethe rotor is turning, a high running torque will be achieved through thecombination of the rotor structure with its magnet of a material ofrelatively high energy product partial ceramic and strong distinctpoles, and the stator arrangement which provides alternating fluxcharacteristics at individual poles.

The rotor may, however, start in the wrong direction. When this occurs,the directional means will stop the motor and start the rotor in theright direction. For example, assume that directional means 30 isarranged to provide continuous running in a counter-clockwise direction.When the rotor is running in this direction, cam 32 will bias pawl 34outward and permit the rotor to rotate. If the rotor starts to turnclockwise, steps of the cam will engage the pawl to stop the rotor andadditionally cause it to rebound and start in the right direction.

The construction of rotor R is such that close tolerance of the hub andthe permanent magnet is readily achieved, especially as regards therotor poles with respect to the stator poles, and additionally thepermanent magnet is securely held by the hub without there being astrong tendency for the magnet to break. In addition, the method offabricating the rotor is relatively low in cost.

As shown, rotor R includes a hub 18, which is comprised of at least twosections, 18 and 18", which carry permanent magnet 17. Section 18'includes a body member and a web 42 having a substantially flat face 44to provide a circular disc 46. The outer periphery of web 42 has achamfered rim 48 extending therefrom and there is an L-shaped flange 50also extending from the outer periphery. Rim 48 also includes a skirt 52extending from the chamfered portion.

Section 18" includes a body portion and a web 62 having a substantiallyflat face 64 providing a circular disc 66. The outer periphery of web 62has a chamfered rim 68 and there is an L-shaped flange 70 extending fromthe outer periphery. As particularly shown in FIG. 3, the chamfered rimsof sections 18' and 18" are adapted to mate one another so that a goodjoint may be provided at least at the outer peripheries. Likewise theL-shaped flanges are adapted to mate one another to provide'an annularspace 41 for permanent magnet 17.

Both sections may be fabricated from a suitable thermoplastic materialsuch as polypropylene, polyamide, polystyrene, polycarbonate, and acetalresins.

As further shown in FIG. 3, the two sections are positioned in spacedrelationship prior to being bonded together. Section 18" is carried by alower support number permanent magnet ring 17 is carried by L- shapedflange 70; and section 18' is brought into contact with section 18"through peripheral skirt 52 by some suitable means (not shown). Heat andpressure is then applied to section 18' such that section 18" can bewelded or otherwise bonded to section 18". principally at the outerperipheries of the circular discs 46 and 66. In accordance with afeature of the present invention, the sections are bonded togetherthrough the application of ultrasonic vibrations. To this end, a meansto transmit the vibrations such as born 82 is brought into workingrelationship with one of the sections (as illustrated in FIG. 3, section18) such that a weld or bond may be effectuated between the twosections, principally at the outer peripheries. Horn 82 is, in practice,attached to an ultrasonic welding head (not shown) in a manner wellknown in the art. The horn is suitably shaped to mate section 18' toreadily transmit vibrations to the section.

The welding head is, in practice, a sonic converter for convertingalternating current into mechanical vibrations at the same frequency.Such frequencies are usually in the ultrasonic range of from 20,000vibrations per second. Horn 82 maintains pressure against the sectionand sets up an ultrasonic wave path therethrough. The vibrations set upat the contact joint between skirt 52 and chambered rim 68 generate heatat or near the joint, causing skirt 52 to melt thus allowing the twosections to join together. The vibrations are continued until thesections are welded together, at least at the outer periphery, to forman integral bond 84 (FIG. 2).

Permanent magnet 17 includes a means preventing angular displacement ofthe magnet with respect to the hub during and after bonding of the twosections together. Means 90 includes at least one recess 92 provided inthe inner wall 94 of the magnet. During the bonding process, materialfrom at least skirt 52 flows into recesses 92 such that the magnet maynot be angularly displaced.

What is claimed is:

l. A method of forming a permanent magnet rotor comprising:

a. providing a hub of at least two sections,

b. positioning a permanent magnet having at least one recess thereinbetween said sections at their outer peripheries, and

c. applying an ultrasonic vibration to at least one of said sections tobond said sections together at their outer peripheries, at least aportion of said sections being melted and flowing into at least saidrecess whereby said permanent magnet is secured in place.

2. A method according to claim 1 wherein said sections are fabricatedfrom plastic.

3. A method according to claim 2 wherein said plastic is a thermoplasticmaterial taken from the group converting essentially of polyprolene,polyamide, polystyrene, polycarbonate, and acetal resins.

UNITED STATES PATENT (PFFECE CERTIFIQATE F QUEQTEUN PATENT NO. 23,881,243

DATED 05/06/75 iNVENTOR(5) 3 Albert C. Bannon It is certified that errorappears in the ab0ve-identified patent and that said Letters Patent arehereby corrected as shown below:

Col. 1, line 52 delete "tow" and substitute therefore two--- Col. 2,line 21 delete ''22" and substitute therefore ---11--- Signed and sealedthis 15th day of July 1975.,

(SEAL) Attest:

C MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officerand Trademarks UNITED STATES PATENT UFFICE (IETI'ETIQATE e memrm PATENTNO. 1 3,881,243

DATED 1 05/05/75 |NVENTOR(5) 3 Albert C. Bannon It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Col. 1, line 52 delete "tow' and substitute therefore two--- Col. 2,line 21 delete "22", and substitute therefore -ll'--- Signed and sealedthis 15th day of July 1975 (SEAL) Attest:

C I-TARSHALL DANN RUTH C. MASON Commissioner of Patents AttestingOfficer and Trademarks

1. A method of forming a permanent magnet rotor comprising: a. providinga hub of at least two sections, b. positioning a permanent magnet havingat least one recess therein between said sections at their outerperipheries, and c. applying an ultrasonic vibration to at least one ofsaid sections to bond said sections together at their outer peripheries,at least a portion of said sections being melted and flowing into atleast said recess whereby said permanent magnet is secured in place. 2.A method according to claim 1 wherein said sections are fabricated fromplastic.
 3. A method according to claim 2 wherein said plastic is athermoplastic material taken from the group converting essentially ofpolyprolene, polyamide, polystyrene, polycarbonate, and acetal resins.